Simplify tail-call optimisation check

Check, that all suspension points are immediately followed by ARETURN
and do not check that all these ARETURNs are immediately preceded by
suspension points.
 #KT-27190 Fixed

compiler/testData/codegen/bytecodeListing/tailcall/tailCallIfReturnUnit.kt

@@ -0,0 +1,16 @@
+// WITH_RUNTIME
+
+import kotlin.coroutines.intrinsics.*
+
+fun check() = true
+
+suspend fun f(i: Int): Unit {
+    return f_2()
+}
+
+private inline suspend fun f_2(): Unit {
+    if (check()) return
+    return suspendCoroutineUninterceptedOrReturn {
+        COROUTINE_SUSPENDED
+    }
+}

compiler/testData/codegen/bytecodeListing/tailcall/tailCallIfReturnUnit.txt

@@ -0,0 +1,6 @@
+@kotlin.Metadata
+public final class TailCallIfReturnUnitKt {
+    public final static method check(): boolean
+    public final static @org.jetbrains.annotations.Nullable method f(p0: int, @org.jetbrains.annotations.NotNull p1: kotlin.coroutines.Continuation): java.lang.Object
+    private synthetic final static method f_2(p0: kotlin.coroutines.Continuation): java.lang.Object
+}